Apparatus for grinding the edges of glass plates



Aug. 3, 1937. L. J-B. FORBES 2,083,737

APPARATUS FOR GRINDING THE EDGES OF GLASS PLATES Filed April 5, 1936 2 Sheets-Sheet l F/GJ.

Aug. 3, 1937. 1.. J-B. FORBES APPARATUS FOR GRINDING THE EDGES OF GLASS PLATES Filed April 3, 1936 2 Sheets-Sheet 2 F/GJ all al Patented Aug. 3, 1937 PATE APPARATUS FOR. GRINDING 'mE limits "or GLASS PLATES Lewis Jex-Blake Forbes, St. Helena, England, as-

signor to Triplex (Northern) pool, England j Liver- ApplicationApril s, 1936. Serial 16 12.51:

In Great Britain April 9,1935

This invention has for its object an apparatus for grinding the periphery of a flat glass plate having a plurality of straight sides with rounded corners.

In apparatus hitherto employedfor this purpose it has been found difllcult to secure smooth grinding of the rounded corners, which frequently have a small radius of curvature, at a considerable distance from the point of support of the plate. When such a corner is being ground, the plate has a tendency to chatter against the grinding wheel, with the result that a succession of fiat surfaces is produced instead of a smooth uniformly curved surface.

In apparatus according to the invention, the edges of plates can be ground smoothly and the grinding pressure is maintained substantially constant, whereby a plate retains the'shape to which it was cut.

According to the invention, the glass plate is attached to the end of a shaft with the plane of the plate at right angles to the shaft; the shaft is slowly rotated and force is applied to a pivoted may be adjustable in position to alter the height of the centre of gravity of the arm. The shaft 5 may carry a template adjustable angularly relatively to the glass plate, the template being adapted to abut against a circular or arcual abutment of approximately the radius of the grinding wheel. The shaft may be rotated by a motor 40 and gearing carried on the arm, and means for reversing the direction of rotation of the shaft may be operated by a device on the shaft so that the shaft is rotated forwards and backwards 55 and 3, the glass plate I (shown in dotted lines' inFigures 1 and 2) is The shaft 4' carries a/wo'rm-wheel i2 (Figure 3) driven by a worm on the shaft l3, which is driven by the chain wheel I through'a worm and wheel in the casing i5 supported on the bracket i6 attached to the bearing block 5. The chain wheel I4 is driven by chain H from the motor i8 mounted on the pivoted arm I. By the above described means the glass plate I carried on the lower end of the pivoted arm I is slowly rotated. An. air passage from the sucker 3 is taken through the collar I! on the shaft 4 to a pipe 20 which passes up the channel I to the exhauster 2| driven by the motor 22, mounted on the upper end of the pivoted arm I.

An arm 23 is fixed to the right hand channel iron 1 along a line through the pivoting point 9 at right angles to the line joining the point 9 with the shaft 4', and a weight 24 is adapted to slide along the arm 23 and to be fixed thereon in any position. By means of the weight" which can be adjusted in height along the left hand channel iron 1, the centre of gravity of the pivoted arm 1, when carrying a glass plate of average weight, is brought to some point on the line of the arm 23, to the right of the-pivoting point 9. There is, then, a torque tending to turnthe pivoted arm I clockwise and thereby to press the edge of the glass plate I against the grinding wheel '21. This torque can be adjusted by means 'of, the weight 24, and, whateverthe position of the, weight 24, the centre of gravity of the pivoted arm 1 is on the horizontal through the pivoting points, when the shaft 4 is vertically below this point.

In operation, the glass plate i is fixed to the sucker frame 2, so that its centre of gravity is approximately in the line of the shaft 4, and; is slowly rotated by the motor l8 while its edge is pressed against the grinding wheel 21. Thereby its whole periphery, including the rounded corners, is ground.

The pressure between the edge of the plate provided that the len h of the arm from the N oi-fries.

pointltotheshaftlandthedistanceofthe grinding wheel 21 from the vertical through the point 8 are suitably proportioned tothe dimenofthelargerpiatesofglass'tobeground. will be explained with reference to Figure Inthis.iigure,B and O representthe'pivot- 18 ac. n W'be the weight of the arm (when cartorque exercised is Wr, and when acting at D,

. the torqueis Wrcos a, and sin a is d/i. If, however, a plate of more than average weight is being ground when thearm isdisplaced to BC, and the excess weight over the average is w, the torque due'to this excess weight is M. There will then be an increase in torque of sod-- Wr(icos a). If thesame plate is narrow in width, .so that, when its minimum radius is being ground the point C is displaced to C" at a distance of d from BC, there will be a diminution in torque of wdf+Wr(l-cos a) Now let it be assumed, takingconditions found in commerce, that the longest plate to be ground is 100 cm. and that the greatest and least widths of plates of this. length-are 50 and 25 cm. respectively, these plates having weights of 6 and 3 kg. respectively, and a maximum radius to ThelengthofthearmBCwillbeassumedtobe I50 cm. The smallest radius to be ground is 25 cm., and the average therefore, 38.5 cm. The grinding wheel 2] should then be 38.5 cm. distant from the shaft 8 when this is vertically below the point 8. That is to say, the distance d and d, for the two plates considered are both 13.5 cm., and the angle a, when the maximum and minimum radii are being ground, is .10'. g The diminution of torque due to the weight W being displaced from D to D is then 0.004 Wr, that is to say, a diminution of 0.4% in the pressure between the plate and the grinding wheel. Now suppose that the smallest plate to be ground so is 25 x 25 cm. with weight 0.8 kg. then the average between the largest and smallest plates is 3.4 kg.and the maximum excess over the average is 2.6 kg. The maximum torque, wd, due to this excess is then 35.1 cm. kg.

as Now, a suitable pressure between the plate and the grinding wheel is 0 kg. corresponding to a torque of 1200 cm. kg. When therefore the plate of 100 x 50 cm. has its maximum radius ground, there is an increase of torque of 35.l-l200 .004 no em. kg. or30.3 cm. kg., namely 2%%. When the plate of 100 x 25 cm. has its minimum radius ground. there is a decrease of torque of 17.5+1200x.004 cm. kg. 'or 22.3 cm. kg., that is to say, less than 2%. These variations in the 86 grinding pressure are negligible in practice because, if the glass plate be cut to the desired shape, they do not produce any appreciable alteration in the shape. In the above it has been assumed that the diameter of the grinding 70 wheel is suiflcient to render negligible variations in pressure due to changes in the point of contact of the plate, with the grinding wheel.

The advantage of this construction, with the centre of gravity located as described, may be as seen from the fact that, if the centre of gravity BCand in. and the angle plate of average weight) acting at D, the

their rounded corners of 52 cm. in the two cases. 1

a,oea,7sv I of the pivoted arm were near to the level of the shaft 4, the pressure of the plate on the grinding wheel would vary approximately as the distance of the shaft from the grinding wheel, so that,

in the case of the plate 100 x 25 cm. the pressure when the.maximum radius was. being ground would be. some four times the pressure when the minimum radius was being ground.

The length of the arm from the pivoting point 3 to the shaft 4 has only a small eifect on the variation in pressure.

1 The weight 2i may be suspended from an arm= 23 having an 'arcual end, so that the torque exercised by the weight does not vary with the inclination of the pivoted arm I. In this case, however, the variations in the grinding pressure are slightly greater.

Constancy of grinding pressure may be secured by an alternative form of the device shown in Figure-i, which shows only the upper portion' of the framework II and the pivoted arm I. The lower portion of the arm I is as shown in Figures 1 and 2. The arm I is pivoted at 8 to a carriage 25 provided with wheels 26 adapted to run on rails 29 carried on the upper frame member I I. Fixed to the carriage 25 is a nut 30 which engages a screw-threaded rod 3| adapted to be rotated by a. motor and gear 32, and provided with bearing 33. Ashort upward projection 34 on the arm I engages a sliding bar 35 by a pin 38 in a slotted hole in' the bar.v The bar 35 is adapted to slide a short distance in the brackets 31 attached to the carriage 25. The bar 35 has two cam surfaces 38 which engage .plungers 33 in switch boxes 40 which constitute a reversing switch in a circuit of the motor 32. In the position shown, neither plunger 40 is depressed, and both switches are open. Y If, now, the inclination of the arm I is increased, the right hand cam surface 38 depresses its plunger 48 to start the motor 32 to turn the rod 3| in a direction which moves the carriage 25, carrying the pivoting point 9, to the right. Thereby the inclination of the arm I is diminished until the inclination shown is regained. Similarly, if the inclination of the arm 1 is lessened, the left hand cam surface 38 operates the motor to turn the rod-3i in the opposite direction, and so to,.-increase the inclination of the arm 1. The device therefore operates to maintain the inclination of the arm 1 constant, by movingits pivoting point 0.

Now, with the arm 1 shown in Figure 4, which is not counterbalanced and, therefore, has its centre of gravity near its lower end, the pressure of the plate on the grinding wheel 21 is determined by the inclination of the arm. Therefore, as the plate is rotated by the shaft 8, so

that the shaft is varying its distance from the grinding wheel, the pivoting point is moved by the device correspondingly, to maintain the inclination of the arm I, and therefore the grinding pressure, always constant.

This device, though more complicated than that of Figures 1 and 2, has the advantage that less height is required in the building.

In all the constructional forms of the appaso located with'reference to the grinding wheel and the shaft that the movement of the shaft, when a plate is being ground, is in a direction which is not far from the centre of the grinding wheel.

Some plates have tobe ground only round a portion of their periphery, as, for instance, round ratus, the pivoting point of the arm is preferably three sides and two corners. For grinding such plates, provision may be made to rotate the shaft 4 forwards and backwards instead of continuously in one direction. The left-hand end of 5 the shaft 4 (Figure 2) carries a boss 4|, to which a disc 42 is attached. Two lugs 43, which can be fixed to the edge of the disc 42 in any positions, are adapted to strike the lever 44 of a reversing switch 45 in the circuit of the motor l8. By this means the motor I8 rotates the shaft 4 in one direction until the switch 45 is operated by one of the lugs 43; it then rotates it in the opposite directionuntil the switch is operated by the other lug 43, and so on.

When a large number of plates have to be ground to the same shape, it is often convenient to grind them to a template, and the accuracy of the shape is not then dependent on the accuracy with which the plates are cut. The template a 46 (Figures 1, 2 and 3) is attached to the boss 4| by bolts 41 which pass through arcual slots in the template, so that its angular position relative to the plate I may be adjusted. The template 46 is adapted to bear against disc 48 (Figure 3) of the same size as the grinding wheel 21 and pivoted concentrically with the grinding wheel on the support 49. It is not essential that the template'should bear against a rotatable disc, and it may bear against a stationary member having its operative portion curved to the radius of the grinding wheel'and placed concentrically with the grinding wheel.

The motor [8 is preferably attached to the pivoted arm 1, as shown in Figures 1 and 2, but it may be carried on the framework II (or in the case of the construction shown in Figure 4, on the carriage 25) and connected by chain to a chain wheel concentric with the pivoting point 9 v The reduction gearing between the motor and the 40 shaft 4 must, however, be carried by the arm, in

order to avoid the driving torque of the motor appreciably affecting the pressure of the plate against the grinding wheel. The effect of the driving torque of a high speed motor carried 45 on the framework may be made negligible.

The exhausting means for the sucker may be independent of the arm, and connection made from it to the sucker by flexible tube. Alternatively, the plate may be secured to the end of 50 the shaft by a vent arm and clamp bearing on the outer surface of the plate.

If, in the construction shown in Figures 1 and 2, the weight of the parts carried by the arm is large compared with the weight of the largest 55 plates to be ground, the height of the centre of gravity is only slightly aifected by variations in the weights of the plates, but the best result is attained by adjusting the height of the centre of gravity as described above, when the arm is 60 carrying a plate of weight intermediate between the extreme weights of a series of plates to be ground.

Having described my invention I declare that what I claim and desire to secure by Letters 65 Patent is:-

1. Apparatus for grinding the periphery of a fiat glass plate comprising, in combination with a grinding wheel, a shaft adapted to be slowly rotated, means for attaching a glass plate to the '70 end of said shaft with the plane of the plate at right angles to the shaft, a pivoted arm carrying the said shaft and adapted to turn inthe direction of the plane of the glass plate, speed reduction gear for driving the shaft fixed on the arm,

75 the centre of gravity of the arm with attached parts being on the side of the pivoting point away from the grinding wheeland approximately at the level of the pivoting point when the shaft is vertically below the pivoting point, and a weight on the arm adjustable in position to alter the duction gear for driving the shaft fixed on the arm, a carriage supporting the pivot of the arm and means adapted to move the carriage to maintain the inclination of .the arm approximately constant as the distance of the shaft from the grinding wheel varies.

3. Apparatus for grinding the periphery of a flat glass plate comprising, in combination with a grinding wheel, a shaft adapted to be slowly rotated, means for attaching a glass plate to the end of said shaft with the plane of the plate at right angles to the shaft, a pivoted arm carrying the said shaft and adapted to turn in the direction of the plane of the glass plate, speed reduction gear for driving the shaft fixed on the arm, the centre of gravity of the arm with attached parts being on the side of the pivoting point away from the grinding wheel and approximately at the level of the pivoting point when the shaft is vertically below the pivoting point, a weight on the arm adjustable in position r to alter the height of the centre of gravity of the arm, a template attached to the shaft, means for adjusting said template angularly relatively to the shaft and an abutment member presenting a surface of approximately the same radius as the grinding wheel against which the template is adapted to abut.

4. Apparatus for grinding the periphery of a flat glass plate comprising, in combination with a grinding wheel, a shaft adapted to be slowly rotated, means for attaching a glass plate'to the end of said shaft with the plane of the plate at right angles to the shaft, a pivoted arm carrying the said shaft and adapted to turn in the direction of the plane of the glass plate, speed reduction gear for driving the shaft fixed on the arm, a carriage supporting the pivot of the arm, means adapted to move the carriage tomaintain the inclination of the arm approximately constant as the distance of the shaft from the grinding Wheel varies, a template attached to the shaft, means for adjusting said template angularly relatively to the shaft and an abutment member presenting a surface of approximately the same radius as the grinding wheel against which the template is adapted to abut.

5. Apparatus for grinding the periphery of a flat glass plate comprising, in combination with a grinding wheel, a shaft adapted to be slowly rotated, means for attaching a glass plate to the end of said shaft with the plane of the plate at right angles to the shaft, a pivoted arm carrying the said shaft and adapted to turn in the direction of the plane of the glass plate, by a motor and gearing carried by the arm adapted to rotate the shaft, means for reversing the di-- 4 forapplying force to the armto move it to press ,the edge of the plate against the grinding wheel with approximately constant pressure. 7

6. Apparatus for grinding the periphery a flat glass plate comprising. incombin'ation with at right angles to the shaft, a pivoted arm carrying the said shaft and adapted to turn in the direction of the plane of the glass plate, by a "motor and gearing carried by the arm adapted to rotate the shaft, means for reversing the direction of rotation of the shaft, means carried by" the shaft adapted to actuate the reversing means to rotate the shaft forwards and backwards through less than a revolution, the centre of gravity of the arm with attached parts being onthe side of the pivoting point away from the grinding wheel and approximately at the level of the pivoting point when the shaft is vertically below the "voting point, and a-weight on the arm adjustable in position to alter the height of the centre of gravity of the arm 7. Apparatus for grinding the periphery of a flat glass plate comprising. in combination with a grinding wheel, a shaft adapted to'be slowly rotated, means for attaching a glass plate to the end of said shaft with the plane of the plate at right angles to the shaft a pivoted arm carry- ,-'ing the said shaft, and adapted to turn in the direction of the plane of the glass plate, by a motor and gearing carried by the arm adapted to rotate the shaft, means for reversing the direction of rotation of the shaft, means carried by the shaft adapted to actuate the reversing means to rotate the shaft forwards and backwards through less than a revolution. a carriage supporting the pivot of the arm and means adapted to move the carriage to maintain the inclination of the arm approximately constant as the distance of the shaft from the grinding wheel varies.

8. Apparatus for grinding the periphery of a flat glass plate comprising, in combination with a grinding wheel, a shaft adapted to be slowly rotated, means for attaching a glass plate to the end of said shaft with the plane of the plate at right angles to the shaft, a pivoted arm carrying the said shaft and adapted to turn inithe direction of the plane of the glass plate, by a motor and gearing carried by the arm adapted to rotate the shaft, means for reversing the direction of rotation of the shaft and means carried by the shaft adapted to actuate the reversing means to rotate the shaft forwards and backwards through less thana revolution, means for applying force to the arm to move it to press the edge of theplate against the grinding wheel with approximately constant pressure, a template attached to the shaft, means for-adjusting said template angularly relatively to the shaft and an abutment member presenting a surface of approximately the same radius as the grinding wheel against which the template is adapted to abut.

9. Apparatus for grinding the periphery of a flat glass plate comprising in combination with end of said shaft with the plane of the plate at right angles to the shaft, apivoted arm carrying the said shaft and adapted to turn in-- the direction of the plane 'of the glass plate, by a motor and gearing carried by the arm adapted ,torotate theshaft, means for reversing the direction of rotation of the shaft, means carried by the shaft adapted to actuate the reversing means to rotate the shaft forwards and backwards through less than a revolution, the centre of gravity of the arm with attached parts being on the side of the vpivoting point away from the grinding wheel and approximately atfthe level of the pivoting point when the shaft is vertically below the piv oting point, a weight on the arm adjustable in position to alter the height of the centre of gravity of the arm, a template attached to the shaft, means for adjusting said template angularly relatively to the shaft and an abutment member presenting a surface of approximately the same flat glass plate comprising, in combination with a grinding wheel, a shaft adapted to be slowly rotated, means for attaching a glass plate to the end of said shaft with the plane of the plate at right angles to the shaft, a pivoted arm carrying the said shaft and adapted to turn in the direction of the plane of the glass plate, by a motor andgearing carried by the arm adapted to rotate the shaft, means for reversing'the direction of rotation of the shaft, means carried by the shaft adapted to actuate the. reversing means to rotate the shaft forwards and backwards through less than a revolution, a carriage supporting the pivot of the arm, means adapted to move the carriage to maintain the inclination of the arm approximately constant as the distance of the shaft from the grinding wheel varies, a template attached to the shaft, means for adJusting said template angularly relatively to the shaft and an abutment member presenting a surface of approximately the same radius as the grinding wheel against arm, and means for app ying force to the arm to I move it to press the edge of the plate against the grinding wheel with approximately constant pressure, said means for applying force to the arm being the weight of the arm with attached parts, and the centre of gravity of the arm with parts being on the side of the pivoting point away from the grinding wheel and approximately at the level of the pivoting point when the shaft is vertically below the pivoting point.

LEWIS TEX-BLAKE FORBES: 

